Need to understand how this Agni motor works

[BigBen]

Uber newb here - my first foray into electric motors and EV. Lots to learn for sure.

I have an Agni 119R motor. I plan to run it at 48v. The data sheet says it does 2600 RPM at 48v. Data sheet says it does 55 RPM per volt. So this would further imply a higher rotation speed at say, 53v (LFP pack - 16S - 55v fully charged). Is it correct that the motor will in fact spin a bit faster at 53/54/55v compared to what the data sheet says - 2600 RPM at 48v ? If this is correct then at 55v x 55rpm = 3025 RPM and at the suggested gearing of 6:1 that they set-up in the plans for the motor mount, this would give a speed of 504 RPM

What I am trying to understand (remember I have 0 experience with electric motors) is, what is the highest speed the motor will turn at 48v and what is the lowest speed it will turn at ? I would have thought that the 2600 RPM at 48v is top end rotation speed? Is this so? (pretty sure it is, but sanity checking here to make sure my assumptions are not half assed)

This motor setup was planned for a boat. Agni supplied the plans to have a motor mount and gearing setup made up locally, but the shaft speed after the 2nd gear reduction is only 433 RPM - what I dont get is, is that the top end rotation speed ? Meaning at that gearing i can't spin the shaft any faster? It really seems this is the way it is, but again making sure I am understanding this correctly.

I am assuming the motor can be controlled by a throttle of some type (wig wag?) and that if 2600 RPM is the top end RPM and it only turns the shaft at 433rpm that I can reduce the rotation speed to a lower RPM to get a slower shaft rotation speed ? I would think that's how it works but since this is my first time delving in to this, I want to make sure I am understanding this correctly with these basic assumptions.

What has me stumped is, given Agni are a well known maker of motors how they could get the final shaft speed of 433RPM so wrong - I need a speed of 975 RPM at the prop at the top end and with the setup supplied I cant get up there - which made me think, perhaps I am not understanding this correctly - perhaps the 2600 RPM is nominal and it can be pushed to higher RPM's so that I can get higher rotation speeds at the prop? I just dont know enough about it all to make these basic assumptions.

This is what I THINK it is - 2600 RPM at 48v is the top end rotation speed at the gearing they gave the plans for and that I can only turn speed down from that point. Meaning 433 RPM at the prop is the highest this setup (as it is designed now) can do and that I can only reduce speed downwards from there - meaning this setup as is, is totally useless. The calcs for my boat suggest 975 RPM shaft speed to push the boat at hull speed (its a displacement hull) so 433 RPM is useless.

I think I will need a redesign of the engine mount/gearing system but before I go that far I just want a sanity check on what i think things are looking like.

One other thing I dont understand - Agni supplied a chart of gearing/1st and 2nd stage RPM's and torque. (chart attached) why is a section of this table in green? It would seem that for some reason (unknown to me at this point) Agni are suggesting that this is the gearing range I should stick too - is that correct?

I am excited and terrified at the same time here. Its exciting to be going electric in the boat but terrifying because I dont know enough about it all yet. Batteries/bussbars/contactors and BMS's are something that I do understand so its not hopeless but Agni have left me stranded here. I am not getting much follow up support from Agni on any of this, so left to try to figure this all out on my own and the assistance of forums like this.

 

[E-HP]

Uber newb here - my first foray into electric motors and EV. Lots to learn for sure.

I have an Agni 119R motor. I plan to run it at 48v. The data sheet says it does 2600 RPM at 48v. Data sheet says it does 55 RPM per volt. So this would further imply a higher rotation speed at say, 53v (LFP pack - 16S - 55v fully charged). Is it correct that the motor will in fact spin a bit faster at 53/54/55v compared to what the data sheet says - 2600 RPM at 48v ? If this is correct then at 55v x 55rpm = 3025 RPM and at the suggested gearing of 6:1 that they set-up in the plans for the motor mount, this would give a speed of 504 RPM

What I am trying to understand (remember I have 0 experience with electric motors) is, what is the highest speed the motor will turn at 48v and what is the lowest speed it will turn at ? I would have thought that the 2600 RPM at 48v is top end rotation speed? Is this so? (pretty sure it is, but sanity checking here to make sure my assumptions are not half assed)

This motor setup was planned for a boat. Agni supplied the plans to have a motor mount and gearing setup made up locally, but the shaft speed after the 2nd gear reduction is only 433 RPM - what I dont get is, is that the top end rotation speed ? Meaning at that gearing i can't spin the shaft any faster? It really seems this is the way it is, but again making sure I am understanding this correctly.

I am assuming the motor can be controlled by a throttle of some type (wig wag?) and that if 2600 RPM is the top end RPM and it only turns the shaft at 433rpm that I can reduce the rotation speed to a lower RPM to get a slower shaft rotation speed ? I would think that's how it works but since this is my first time delving in to this, I want to make sure I am understanding this correctly with these basic assumptions.

What has me stumped is, given Agni are a well known maker of motors how they could get the final shaft speed of 433RPM so wrong - I need a speed of 975 RPM at the prop at the top end and with the setup supplied I cant get up there - which made me think, perhaps I am not understanding this correctly - perhaps the 2600 RPM is nominal and it can be pushed to higher RPM's so that I can get higher rotation speeds at the prop? I just dont know enough about it all to make these basic assumptions.

This is what I THINK it is - 2600 RPM at 48v is the top end rotation speed at the gearing they gave the plans for and that I can only turn speed down from that point. Meaning 433 RPM at the prop is the highest this setup (as it is designed now) can do and that I can only reduce speed downwards from there - meaning this setup as is, is totally useless. The calcs for my boat suggest 975 RPM shaft speed to push the boat at hull speed (its a displacement hull) so 433 RPM is useless.

I think I will need a redesign of the engine mount/gearing system but before I go that far I just want a sanity check on what i think things are looking like.

One other thing I dont understand - Agni supplied a chart of gearing/1st and 2nd stage RPM's and torque. (chart attached) why is a section of this table in green? It would seem that for some reason (unknown to me at this point) Agni are suggesting that this is the gearing range I should stick too - is that correct?

I am excited and terrified at the same time here. Its exciting to be going electric in the boat but terrifying because I dont know enough about it all yet. Batteries/bussbars/contactors and BMS's are something that I do understand so its not hopeless but Agni have left me stranded here. I am not getting much follow up support from Agni on any of this, so left to try to figure this all out on my own and the assistance of forums like this.

Sorry, I couldn’t read through the whole post but perhaps this might help. If your battery is charged to 48v, and full throttle is applied, the motor sees 48v coming from the controller. If you apply zero throttle, the motor sees 0v. If you apply half throttle, the motor sees 24v. The motor will always turn at an rpm based on the motor constant and the voltage applied, at no load. The controller uses pulse width modulation to change the effective voltage going to the motor. Note that a fully charged 48v battery (54.6v) will spin the motor faster than when nominally charged to 48v, and slower when low on charge.

 

[BigBen]

thanks for the reply. It does help a little. I am pretty sure I have this but checking in case I have it all wrong. Its a little embarrassing to ask such a basic question - however i Need to make sure I am understanding things correctly.

Re the long post. I do get that long posts dont get replied to much. Found it hard to say in 20 words or less but thanks again for you input. Appreciated.

 

[E-HP]

thanks for the reply. It does help a little. I am pretty sure I have this but checking in case I have it all wrong. Its a little embarrassing to ask such a basic question - however i Need to make sure I am understanding things correctly.

Re the long post. I do get that long posts dont get replied to much. Found it hard to say in 20 words or less but thanks again for you input. Appreciated.

I believe understanding how the motor constant works (more voltage = higher rpm) addresses most of the things in your post. However, note that this relationship assumes no load. With prop in the water, there’s obviously load in order to propel the boat forward. That will take power, not only voltage, but even with a lot of power you still won’t achieve the no load rpm, so you need to factor that into your design.

 

[BigBen]

Thanks again for your input - helps immensely. Long learning curve ahead but keen to do a deep dive into the weeds. Guess I am preaching to the converted on this forum but electric motors for motion is fascinating !

 

[amberwolf]

If the motor spins a certain rpm per volt, you simply multiply that kV (RPM/volt) by the volts it is provided, and that tells you the unloaded speed of the motor.

The speed it will go when actually riding will depend on a bunch of things--actual load caused by riding conditions / weight / etc, actual power avialable from the battery and controller, actaul voltage after sag caused by load, etc. I'd recommend taking the basic system info and your riding conditions to a simulator or calculator to help you make guesstimates--it will take some time to learn whatever sim / calc is used to apply it to your needs, but is worth the time to learn as it will teach you in general how systems work vs riding conditions, etc. I don't have a link to a boat / water sim or calc, but there should be some out htere even if they are not specificaly for electric.


Once you know the motor rpm, then multiply that by your gearing to get shaft rpm. If that rpm is too low, you can either increase system voltage to give a motor rpm that will work with the gear ratio you already have, or you can change the gear ratio to get that speed.

keep in mind that whenever you use gearing to decrease speed, you are increasing torque. if it takes a certain amount of torque to spin your prop in your conditions, then the *inverse* gearing ratio x motor torque must provide at least that much. meaning when you figure prop speed you use the regular gearing ratio (that gears speed down) but when you figure prop torque yo uswap the ratio numbers because it gears torque up.

if the gearing makes speed go up instead of down, then it makes torque go down, instead of up.

 

[BigBen]

WOW - light bulb moment for me. So some of the pieces I have been trying to understand just fell into place from the info you just supplied. Thanks!

Lots of reading later its all making more sense now.

Still lots to figure out - busy hunting down more material to read